Drinking alcohol causes a pleasant feeling because it releases endorphins, the brain’s natural opioids. But a new study has found that problem drinkers differ from social drinkers in the way alcohol affects one part of the brain. The report appeared Wednesday in Science Translational Medicine. Researchers performed PET imaging on 13 heavy drinkers and 12 social drinkers after each had had a standardized amount of alcohol. The scientists traced the release of endorphins in two regions of the brain — the nucleus accumbens and the orbitofrontal cortex.